Neural probe design for reduced tissue encapsulation in CNS

This study investigated relationships between a microscale neural probe's size and shape and its chronic reactive tissue response. Parylene-based probes were microfabricated with a thick shank (48 μm by 68 μm) and an integrated thin lateral platform (5 μm by 100 μm, either solid or one of three lattice sizes). Devices were implanted in rat cerebral cortex for 4 weeks before immunostaining for neurons, astrocytes, microglia, fibronectin, laminin, and neurofilament. While nonneuronal density (NND) generally increased and neuronal density decreased within 75 μm of a probe interface compared to unimplanted control regions, there were significant differential tissue responses within 25 μm of the platform's lateral edge compared to the shank. The NND in this region of the lateral edge was less than one-third of the corresponding region of the shank (129% and 425% increase, respectively). Moreover, neuronal density around the platform lateral edge was about one-third higher than at the shank (0.70 and 0.52 relative to control, respectively). Also, microglia reactivity and extracellular protein deposition was reduced at the lateral edge. There were no significant differences among platform designs. These results suggest that neural probe geometry is an important parameter for reducing chronic tissue encapsulation.